Clinical application of neutron radiotherapy has expanded rapidly in recent years, but progress in precision neutron dosimetry has been hampered by a lack of basic nuclear physics data. The problem is most severe for those clinical facilities which produce neutron spectra having a substantial fraction of neutrons with energy greater than 20 MeV. In this energy region there is no adequate data base for the calculation of significant dosimetry quantities such as the relative response of "tissue-equivalent" dosimeters. These calculations are required if the delivered dose to tissues of various chemical composition is to be related with confidence to the dosimeter response. Until recently, few laboratories were equipped to perform the required measurements. Ohio University, in conjunction with Lawrence Livermore Laboratory, is developing a new magnetic-quadrupole-triplet spectrometer. This spectrometer will be used with the Ohio University intense neutron source to provide an efficient, flexible technique for the measurement of neutron-induced reactions. Specifically, we propose to measure the angle- and energy-dependent cross sections for the production of protons protons, deuterons and alpha particles by 20-26 MeV neutrons incident on carbon, nitrogen and oxygen. Moreover, an effort will be made to measure directly the entire energy spectrum (1.0 less than Ep, alpha less than 26 MeV) of charged particles produced by high energy neutrons incident on tissue-equivalent plastics, e.g., Shonka plastic A-150. Such a measurement would provide both an internal consistency check on the individual measurements and a direct determination of the quantities most relevant to neutron dosimetry.